Level and the like.



A. C. W. ALDIS.

LEVEL AND THE LIKE. APPLICATION FILED JUNE'I,1911.

Patented June 3, "1913.

3 SHEETS-SHEET 1.

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A. c. w. ALDIS. LEVEL AND THE LIKE. APPLICATION I'ILED JUNE 7 1911.

3 SHEETS-SHEET 2.

Ill 7IIII INVENTOR Arfhur Cyril WebbA r ATTORNEYS Patented June 3, i913.

UNITED STATES YPATENT OFFICE. v

, ARTHUR CYRIL WEBB ALDIS, OF BIRMINGHAM, ENGLAND.

LEVEL AND THE LIKE.

. To all whom it may concern:

Be it known that I, ARTHUR CYRIL WEBB Arms, subject of the King of Great Brit-- ain, residing at Old Gran e Road, Sparkhill, Birmingham, Englan manufacturing optician, have invented certain new and useful Improvements Relating to Levels and the Like, of which the following is a specification.

This invention has for its object to provide improved levels and like instruments.

depending for their operation upon the movements of a fluid bubble.

The invention comprises the employment of the fluid bubble in an optical system to act as a lens, that is, the surface of the bubble forms one of the refractive or reflective surfaces in an optical system, and the arrangement of such system so that the movementsof an image due to displacement of the bubblecan be viewed directly or by project-ion on a screen.

In the three accompanying sheets of explanatory drawings; Figure 1 is a vertical section of an optical level constructed inaccordance with this invention. Figs. 2 and are side elevation and vertical section respectively of another form of optical level specially adapted for use in submarine vessels. Fig. 4 is a vertical section and Fig. 5, a diagrammatic. plan of an optical level adapted for engineers and surveyors, while Fig. 6 is a vertical section of an elaborated form of such level adapted for use, more especially in the setting of astronomical instruments. Fig. 7 is a vertical section showing an adaptation of the invention to serve as a vibrascop Fig. 8 illustrates the combination of a level with a telescope. Figs. 9 and 10 are part sectional elevation and plan showingthe application of the invention to clinometers for gun laying and like purposes, and Fig. 11 is a section to a larger scale of the level alone.

The same reference letters in the different views indicate the same or similar parts.

In the application of the invention to a simple form of optical level as shown in Fig. 1 adapted for project-ion of an image on a screen, I employ a small closed cylindr cal tube a containing transparent liquid similar to an ordinary level but referably with a smaller and approximate y spherical bubble. This is mounted in conjunction with a Specification of Letters Patent.

focus on a screen 0 the image of the incan-- descent filament d of a lamp 0 formed by the bubble. This combination of lamp and condenser ismounted in a vertical brass Patented June 3, 1913..

Application filed June-7, 1911. Serial No. 631,714.

tube 7 the top part of which g contains the v lamp holder. h and slides on the part 1 in the form of a cap so as to facilitate the 1 changing of lamps. The screen '0 is arranged in fixed relation to the tube or projector f in any convenient manner.

The image transmitted through theibubble and the condenser b will show an end elevation of the filament asviewed from a point on the axis vertically below the lamp. In order that a convenient and clear index mark might be obtained the filament should be in-the form either of a single straight line or else a sharp V perpendicular to the axis of the instrument. Also the tip of the electric bulb should be situated at the side to avoid distort-ion of the image of the filament;

lVhema tubular level as a is employed it is supported at its two ends so that the curved axis of the level lies in a diametral plane which in the drawing is the plane of the paper. The condenser b is made of sufficiently large aperture to include complete pencils transmitted from the lamp through the bubble even when the latter is displaced to the limit of its motion. The bubble forms an air lens of strong negative power and consequently gives a virtual image of the filament immediately above the level for all displaced positions.- The lens I) must therefore be designed so that the conjugate of this virtual image lies approximately on the screen a. v

- A stop a is located below the lens I) at any suitable position. By thus providing a restricted aperture for the passage of the pencils the resultant image is rendered free from spherical aberration and consequently gives a well defined index mark. Since the tube of liquid a forms part of the optical system transmitting the image itis evident that the resultantimage will suflier severely from astigmatism, but since a straight line index mark perpendicular to the plane of the paper only is required the condenser I) can be adjusted so as to focus this focal line on the screen and no loss of sharpness or brilliancy will be detected.

Figs. 2 and 3 illustrate a tubular optical level designed especially for submarine vessels, and the more complex arrangement there represented is adapted to combine the following features: (a) The image moves in the same direction as the bubble. (b) The image forms a vertical line having a horizontal motion along a narrow vertical screen placed level with the observers eye. (a) No lens elements need be of larger aperture than the total length of the level a itself. ((Z) The image can be focused and also centered in the case where the screen is rigidly fixed and marked with a scale and zero position. (6) The lens system employed for reversing the motion of the image embodies the principle of the well known erecting eye piece, and consequently affords a fiat field so that the index mark is clearly and sharply defined in its extreme positions as well as in the central position. Since in a submarine it is the level of the whole vessel that has to be indicated it is evident that the rigid connection between .the instrument and the screen is provided by the vessel within which they are fitted, and hence the motion of the bubble can be very largely magnified and a greatly amplified motion shown on a screen of large dimensions.

Referring to Figs. 2 and 3, e is a tubular electric lamp or roof-lamp which preferably presents a straight line of incandescent filament. The lamp is mounted in a small detachable box at the top of the projector tube 7 in a manner which permits of ready replacement of burned out lamps. Two planoconvex condensers b are placed with their convex sides immediately adjacent to the tubular level a which is mounted in a short metal cylinder which acts as a distance piece between the said lenses. The mounting for the lenses 7) and level a is arranged so as to insure the axis of the level being fixed in a plane perpendicularor at right angles to the line of the filament in the lamp 6. In conjunction with the lenses 6 are I coaxially mounted three small equal lano-convex lenses j, is, Z, and one larger double convex lens m which latter is optically equivalent to the two condenser lenses I) placed with their plane sides together. The adjustments are such that the center of the lens m and the upper condenser lens I) are equi-conjugates forthe compound lens made up of the two lenses y'and k which are situated approximately equi-distant from the level a and the lens m and are placed symmetrically with piano sides adjacent. Thus since the bubble forms a virtual image of the filament immediately above the level a, the conjugate of this virtual image formed by the 'two lenses 7' and k will always lie in the central plane of the lens m which is approximately 7 at the focus of either lens 70 and Z the latter being also placed symmetrically with regard to the lens m with convex sidesadjacent.

The filament of the lamp e is placed at the focus of the upper condenser lens 5 so i and m form an approximately symmetrical pattern about the plane of the stop at the point i which is situated midwa between the two lenses j and is. As rega-r s the lens Z this is mounted in a focusing cell' a which screws on the lower end of the projector tube f in the form of a cap and is provided with a lock ring 0 to fix it when the image has been focused on the screen. By means of a mirror p (or a'totally reflecting prism) pivoted by links 9 on the projector tube the image is deflected to a vertical screen (not shown) the movement of the image on the screen being then in 'a horizontal direction. The connection of the links 9 with the tube f is effected by a ring 1' which can be rotated slightly with respect to the tube. By this means the image can be readily set to the zero position or to any graduation on the screen. A flange 8 enables the instrument to be securely bolted to a horizontal bracket which is preferably rigidly fixed to the roof of the vessel.

A simple spherical optical level designed for direct visual observation of the image of a pair of cross lines and adapted for the purposes of engineers and surveyors is shown in Fig. 4. Two thick lenses a and a are worked so that they form an optical contact around the portions of their surfaces in contact. The lens.a has a central cavity ground thereon for the reception of the liquid. By the use of optically ground surfaces between the abutting portions of the lenses the liquid is effectively sealed and leakage prevented. The upper surface of a is plane and has marked on it two fine lines intersecting at right angles on the axis of the instrument, while the lower surface of a is polished and silvered, forming when viewedfrom above a shallow concave mirror. The two lenses a and a. are tightly clamped together in a metal holder 7 by means of a clamp t with a. continuous coil spring a interposed between it and the upper plane sur-' and contraction of the glass'and brass elements.

The optical arrangement of the level shown in Fig. 4 is such that the concave surface of the upper lens (1 lies just below the focus 1) of the bottom mirror, while the u per surface of that lens is situated considerably above it. Consequently the image of the cross lines on a seen in the bottom mirror through the parts of the liquid lens not obstructed by the bubble lies at a point w some distance above the upper surface of a, and thls 1mage affords a ready means for -with. the linel, 3.

centering the eye (situated at as) accurately 011 the axis of the instrument and so obviating errors in estimating centrality due to parallax. proper position, the bubble is adjusted so that the images of both cross lines seen through it are coincident with the original cross lines on the upper surface of a. Now

'since the image of the. cross lines due to the and roughly leveling the instrument it is sufficient to move the small bubble until it appears central. For greater accuracy the very much enlarged image of the bubble as seen by reflection .in the .bottom of the level can be used, while for the greatest accuracy the eye is centered by means of the cross lines and their reflected image viewed through the liquid, and thenthe image of the cross lines seen through the bubble by reflection at the mirror is brought into exact coincidence with their intersection.

Fig. 4. shows the bubble slightly displaced and Fig. 5 shows what-is seen when the eye is centered above such a level with the hubble slightly displaced in the'direction of one of the cross lines. The circle 1, 2, 3, 4, represents the outer edge of the top lens a, and thelines 1, '3, 2, 4, are the two cross lines traced on it. 5 is the bubble which is slightly displaced along 4, 2. The eccentric circle 6 represents the enlarged reflectedimage of the bubble and the thicker radial lines between it and the outer circle represent enlarged images of the portions of the lines 1, 3, and 2, 4, seen in the reflector outside the bubble. The coincidence of such thick portions ofthe lines with thin i nter-' secting portions indicates that the observers eye is centered. The (curved line 7 is the image on that portion of the line 1, 3, which is seen through the bubble and indicates that the'bubble is not central. As the bubble is broughtto' its: central position this line rapidly straighten's out until it coincides The strong curvature of the lines as viewed through the bubble in all but the central. position forms a very accurate means of detecting an error of level.

Fig. 6 shows an optical level for obtaining the highest sensitiveness while affording that quick motion which can always be ob-' tained with levels of small size employing comparatively strong curvatures, The evel is more especially adapted for the setting of The viewing in- The eye having taken up its carefully leveling the s'trument is an ordinary compound microscope 8 with its objective placed immediately above a small spherical level a a. designed similarly to that shown in Fig. 4 as regards the method of sealing the alcohol in a double convex cavity. In this case, however, the top glass 0 is thin, both the cavity and the bubble are very small and the bubble travels on a very shallow concave surface at the underside of the lens a. The lower glass a vhas its under surface perfectly. opaque except for a small hemispherical cavity polished in its center. Immediately below this central cavity there is mounted a small double concave negative lens 9, and below this is situated a small central stop 10 and a detachable electric lamp 0. The whole of the optical arrangement is rigidly mounted at right angles to a suitable base plate 11. The lens 9, the small cavity in the base of a together with 'the powerful diverging effect of the small bubble all tend to result in a very small image ofthe illuminated stop 10 being seen in the eye piece, and produce, what is sometimes known as an artificial star. When the image of this sto due to the bubble is adjusted so as to be in the focal plane of the compound microscope very small displacements of the image will be rendered abundantly evident by the compoundmicroscope, and they may be read elf on a micrometer contained in the eyepiece of the instrument. So sensitive. can such a level be made that it can readily be adapted to act as a vibrascope. To render it efficient for that purpose, however,

the following modifications should be introduced. The spherical level itself should be made larger and the curvature of the surface over whichthe bubble moves much steeper in order to avoid the trouble of instrument for bringing the spot of light into the field of view of the microscope. The bubble should be as large as the microscope will admit. By such means the level is rendered comparatively insensitive considered only as a level, but the bubble will be very sensitive to vibration owing to the inertia of the large mass ofsurrounding liquid, and such vibra- 'tions aremade very apparent by the microscope viewing theimage of the illuminated stop 10. Such an instrument can obviously be standardized in all its parts and there-j fore a set of vibrascopes made all of which will show the same amplitude of motion in the eye piece whensubject to identical tremors. It is very difficult, however, to provide a large; level with a large bubble and at the same time get the objefct glass of a high power compoundmicroscope sut'fi-- ciently close for viewing the image produced by refraction through the bubble. To obviate this difliculty I have devised a. special form of vibra'scope as shown in Fig; 7.

In this case the image of a small incandescent filament in a lamp is viewed by reflection in the cavity of a comparatively large bubble in the level a. A spherical level with a known type of'sealed metallic reservoir will be quite suitable, but the curvature of the surface over which the'bubble travels should be large in order to avoid the trouble of having'to adjust the bubble very carefully to the central position.

The image of the filament produced by 'reflection in'the bubble is situated above the level and can therefore readily be viewed even by a very high power microscope as represented by 8. As the deflections of the reflected rays due to tremors of the bubble are very much more marked than the deflections of the refracted rays, the mstrument shown in Fig. 7 is exceedingly sensitive to tremors. It possesses thelimitation,

however, that it only affords readings of tremors in the plane of the reflection since the image by reflection suffers very greatly i signed on the lines of Pi 6 indicate at v prism 18 once the amount and-direction of the maximum oscillation. The vibrascope shown in Fig. 7 can also obviously be standardized, and thus the readings of different. instruments used for comparative tests.

A useful form of optical level adapted as an attachment for a telescope is shown in- Fig. 8. It consists of a short vertical tube fmounted on a ring or collar 14 which lat:

teris adapted for attachment tothe objec-- tive end of a telescope 15 so that when the axis of the telescope is horizontal the axis of the short tube 7 is vertical. At its upper end the tube f is closed except for a small central stopjor aperture as shown. Below the stop or aperture about half way down the tube f is placed a small tube or'trans parent spherical level a, and below this again is arranged a positive lens I) so placed thatthe'image of the aperture due to the bubble is at the focus of the lens 6. The latter will therefore form an image of the aperture as seen through the bubble at infinity, and this can be viewed by the telescope 15 simultaneously with any other distant external objects, the said image being directed by means of the. total reflecting placed opposite the upper portion of the telescope objective. It should be noted that the attachment is of small size in comparison with the telescope, and consequently the small prism diminishes only slightly the brilliancy of the image of ex- Such a device as that two flat glass plates a ternal objects as seen by the eye. Superimposed on this image there would be a sharp image of the stop or aperture which image would move over a Wide visualangle for comparatively slight displacements of the telescope axis. If, therefore, the telescope is fitted with crosswires the telescope could be quickly and accurately leveled by causing the spot image of the aperture to come centrally on the cross wires.

above described is evidently of great use as a clinometer for gun sights, enabling the one telescope to act both as sight for aiming at a target and also as clinometer for aiming at an invisible target-by means of sight elevation. The device is especially advantageous in naval gunnery since in these operations it is imperative to have a level which will immediately respond to and accurately indicate the changes in inclination which are continually occurring in a moving vessel. For the-precision required, however, in modern gun sighting it is necessary to obtain the utmost refinements in order to secure apparatus sufliciently accurate and sensitive.

Figs. 9, 10 and 11 show apparatus designed to give the aforesaid accuracy and to afford an artificial horizon visible in the instrument-quite independently of the ordinary telescopic sight, andmoreover mounted in a convenient manner for the purpose of gun laying under the ordinary conditions of naval practice. The level employed is a spherical level designed for a high degree of accuracy and sensitiveness. Though essentially a spherical level the cavity containing the bubble is purposely made longer in one direction than at right angles to it so as to afford a very small degree of free motion of the bubble in a lateral direction and a more extended motion in a longitudinal direction. The level is formed by clamping together cal contact at the adjacent plane surfaces, the upper one having a small spherical cavity ground and polished in it and exactly opposite this there is a corresponding spherical cavity of very much stronger curvature ground and polished in the lower plate. The deep cavity in the lower plate is, however, partially filled up with cement as indicated by a in order to form a long cavity or chans nel within which the very small bubble can travel. In the instrument shown the bubble has about four degrees total travel in the longitudinal direction, andonly one or two degrees of motion at right angles to this. Cross wires are placed vertically below the level and brightly illuminated either by an electric lamp withfrosted bulb or by means of a lens 16 in conjunction with a mirror 17 placed at an angle of forty-five degrees. The lens and mirror focus 011 the cross wires a worked to an optithe light coming from the opening toward which the telescopic sight is directed. Immediately above the level is mounted a total reflecting prism 18 which enables the image of the cross wires due to the bubble to be focused by a microscope 19. The whole is rigidly mounted on an arc clinometer 20. The latter enables the angle of sight to be very accurately set, the adjustment-being such that the axis of the microscope should indicate the true horizontal position when the telescopic finder is laid on the target.

The fixed base of the clinometer is attached to a long bar 21 which slides on a supporting bracket 22. The bar is accurately mounted so that it always lies exactly parallel with the axis of the telescopic sight. The microscope is set either absolutely parallel with this direction or at a small elevation according to the desired angle of sight by means of the arc clinometer 20. Both the telescopic sight and the bar carrying the optical level may be arranged to slide in their supports so that either can be conveniently drawn forward or pushed backward according to which the gun-layer decides to use. The microscope transmits to the 0bservers eye a greatly magnified image of the cross wires formed by the bubble and the minute displacements of the bubble give rise to very large displacements as seen in the field of view of the microscope. The eye piece is provided with fixed cross wires. In actual practice, after the sight has been set according to the instructions received from the range finders, the gun-layer adjusts his gun so that the moving image of the cross wires seen in the microscope coincides with the fixed cross wires in the eye piece. The gun is then correctly laid in the required position for firing.

The invention is not limited to the purposes or -modes of application herein described as it may also be applied for various other uses provided that in all cases the bubble serves as a lens in the associated optical system.

Having thus described my invention what image due to displacement of the bubble can be viewed, substantially as described.

3. In levels and the like, the combination comprising a pair of lenses'formed with an intermediate cavity containing fluid and a bubble, and means whereby movements of an image due to displacement of the bubble can be viewed,.substantially as described.

4. In levels and the like, the combination of an optical system consisting in part of a bubble arranged to act as a lens; means for directing light through the bubble, and means whereby movements of an image due to displacements of the bubble can be viewed, substantially as described.

' 5. In levels and the like, the combination of an optical system consisting in part of a bubble arranged to act as a lens; a lamp situated on one side of the bubble, a condenser on the bther side of the bubble, and a screen for receiving an image produced by the bubble, substantially as described.

6-. In levels and the like, the combination of an optical system-consisting in part of a bubble arranged to act as a lens; condenser lenses mounted on opposite sides of the bubble, a lamp on one side of the bubble, a reversing lens system, a condenser and focusing lens situated on the opposite side of the bubble, and a screen, substantially as described.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ARTHUR CYRIL VVEBBALDIS.

Witnesses:

JOHN MORGAN, FRANCIS MALPAs. 

